In production of glass substrate, surfaces of glass substrates are generally scanned by a laser scanner to determine whether there is debris thereon or not. Normally, a laser scanner for raw glass substrate is used, and a platform thereof is mounted with a plurality of pins to support the glass substrate, such as shown in FIG. 1. FIG. 1 is a structural and illustration view of a prior art inspecting device for detecting whether there is an appearance of debris on a surface of a glass substrate and which is the main configuration of the laser scanner for raw glass substrate for determining whether there is debris appeared on a surface of a glass substrate. A platform 12 is neatly mounted with a plurality of pins 15 for supporting a glass substrate 14. The glass substrate 14 is transferred by rollers, and sometimes traces are marked down on the underside of the glass substrate 14 during displacement. When an existing laser scanner is used to conduct a scanning over a top surface of the glass substrate 14 to determine whether there is an appearance of debris, a laser unit 11 will project laser beams toward the top surface of the glass substrate 14, and the laser beam will further reach to the underside of the glass substrate after refraction. Then, a charge-coupled device (CCD) image sensor 13 will be used to collect the reflected laser beam. However, not only the reflected beam from the top surface of the glass substrate 14 will be collected, but also the reflected laser beam from the underside will be collected. The traces 19 marked on the underside of the glass substrate 14 could be mistakenly interpreted that there is debris 18 appeared on the top surface of the glass substrate 14, such as shown in FIG. 2. FIG. 2 is a scanning result after the inspecting device of FIG. 1 completes its scanning over the glass substrate. It can readily see that it not only demonstrates there is an appearance of debris 18 on the top surface, but also demonstrates the appearance of the traces 19 from the underside of the glass substrate 14. This scanning result will cause the laser scanner to mistakenly interpret that the glass substrate 14 is defective and a cleaning process, or reworking is needed. In worst scenario, the glass substrate 14 could mistakenly be trashed away. The mass production will be negatively affected. As a result, there is a necessity to improve the existing laser scanner for raw glass substrate so as to effectively eliminate the unwanted interference caused by the reflected laser beam from the underside of the glass substrate.